Generally, nail guns have an air chamber for collecting pressurized air from an air source as a power source for nail guns and a cylinder mounted in a housing. The cylinder may be movably relative to the housing or be fixed on the housing. The cylinder includes a piston slidably disposed therein. The piston divides an inner chamber of the cylinder into a top cylinder chamber and a lower cylinder chamber. The nail gun also includes a trigger valve that is capable of being triggered by pressing so as to drive nail hitting action of the nail gun. The pressurized air in the air chamber enters into the top cylinder chamber to press the piston move downwardly when a trigger of the trigger valve is pressed. The pressurized air in the top cylinder chamber vents from the top cylinder chamber and enters into the lower cylinder chamber to drive the piston move upwardly to its original position.
Nail guns employing movable cylinders have been developed, for example, U.S. Pat. No. 4,784,308, U.S. Pat. No. 4,319,705 and U.S. Pat. No. 4,294,391 disclose a nail gun employing a movable main valve and a movable cylinder separated from the main valve. The main valve can move downwardly or upwardly together with the cylinder. Specifically, the pressurized air in the air chamber drives the main valve and the cylinder to move upwardly when the trigger is pressed. As such, the air venting passage of the lower cylinder chamber, and the air flow passage between the main valve and the cylinder are opened. As a result, the pressurized air in the air chamber enters into the top cylinder chamber to move the piston downwardly to hit the nail. The main valve drives the cylinder move downwardly to its original position when the trigger is released. In this instance, the upper air venting passage is opened such that the piston move upwardly back to its original position.
In each of the aforementioned nail guns employing movable main valves and movable cylinders, an air flow passage is employed to conduct pressurized air to drive the main valve and the cylinder to move so as to control the piston moving upwardly back to its original position. In addition, the air flow passage is formed in a number of separate parts, for example, movable cylinder, inner sidewall of the housing and a bushing disposed around the cylinder. The structure of the air flow passage is too complicated. As a result, controlling of nail hitting of the nail gun is unstable. This issue becomes significant especially after the nail gun has been used for a period due to abrasion between different parts. In addition, a cost of manufacturing such an air flow passage is also very high. Therefore, there is a desire to provide a nail gun employing movable main valve and movable cylinder which can achieve a high stability of controlling of nail hitting.